Magnetic Force fields
You can change the strength of each magnetic field independently to allow for variation. Use the "Strength" input to determine the force of the field. 

Along with the strength value, you can also change values such as noise, the seed of the noise, flow and collision to fine tune the force fields to your liking.

Refer to the Blender Documentation for more information on force fields in Blender.

If you want a magnetic force field to push objects instead of pulling them, you can input a negative value in the strength input.



To select a force field, you can either find it in the objects list (The list at the top-right of your screen by default) or click on the empty object in your 3D view (An empty object is a coordinate rather than a mesh). It should look like this in your 3D view:


Hope this helps.